This invention relates generally to a draft control system for an agricultural tractor and more particularly to a draft control system for a hydrostatic drive tractor wherein the hydrostatic drive pressure is sensed to adjust the hitch to vary the working depth of an implement so as to not exceed a maximum draft load and draft depth.
In the past, tractors have been provided with hydraulic lift systems for automatically raising or lowering an associated integral or semi-integral implement in order to maintain a substantially constant implement draft or draft load on the tractor. The draft load on the tractor has been generally sensed as a force exerted on the draft links of the tractor as shown in the Du Shane U.S. Pat. No. 2,940,530 granted on June 14, 1960.
In tractors having main drive wheels mechanically connected to the engine, a complex torque sensing coupling had to be interposed in the drive line between the engines and the wheels as shown in the McKeon U.S. Pat. No. 3,575,241 granted on Apr. 20, 1971.